Abstract

The Minnesota Multiphasic Personality Inventory-2 (MMPI-2) is a popular assessment tool used for the psychosocial assessment of personal injury litigants. However, there are inherent structural problems found in the MMPI-2 that question the utility of this test. In 2006, Goh restructured the MMPI-2 at the item level in order to provide a more accurate and reliable assessment device. Using a large sample of personal injury litigants, Goh rebuilt the MMPI-2’s scoring and analysis system specifically for the psychosocial assessment of personal injury litigants. Called the Minnesota Multiphasic Personality Inventory-2 for use with personal injury litigants (MMPI-2-PI), the development of the MMPI-2-PI used contemporary methods with the goal of enhancing internal consistency and eliminating item overlap. A unique feature of the MMPI-2-PI were items that were weighted according to the relevance of the constructs they measured which resulted in independently weighted scales and subscales. Since Goh’s initial restructuring of the MMPI-2, Ben-Porath and Tellegen (2008) developed the Minnesota Multiphasic Personality Inventory-2-Restructured Form (MMPI-2-RF) also using contemporary methods to restructure the MMPI-2. Published in 2008, the MMPI-2-RF was developed as an alternative version of the MMPI-2 for routine clinical psychosocial evaluation. While the MMPI-2-PI appeared to be a promising new approach for assessing personal injury litigants, it was still in its infancy. As such, the goals of this dissertation were to examine the Incremental validity and clinical utility of the MMPI-2-PI by comparing it to the more traditional MMPI-2 and more contemporary MMPI-2-RF. Using a sample of 2,989 personal injury litigants, analysis of the MMPI-2-PI included two comparisons: one with the MMPI-2-PI and MMPI-2; and the second between the MMPI-2-PI and the MMPI-2-RF. Comparisons between the MMPI-2-PI and the MMPI-2 demonstrated improved Incremental validity and
interpretability for the MMPI-2-PI. This comparison not only showed the MMPI-2-PI to be comparable to the MMPI-2, but also to be a better measurement device while demonstrating no evident scale redundancy and clear delineation of the constructs being measured. The second comparison indicated the MMPI-2-PI showed comparability to the MMPI-2-RF in assessing similar constructs. However, given some redundancy issues were evident in the MMPI-2-RF, incremental improvement was indicated for the MMPI-2-PI in assessing personal injury litigants. Further examination of the clinical and interpretive implications of using the MMPI-2-PI provided information on what constructs are more common (and not so common) within a medico-legal setting. Further to this, the majority of MMPI-2-PI scales and subscales demonstrated sensitivity to the constructs they were measuring and the diagnostic groups commonly seen in medico-legal evaluations. Independant interpretation of the majority of the MMPI-2-PI subscales was also demonstrated and recommended given there were different item weightings between the scales and subscales. This was an important consideration, given the subscales of the more traditional MMPI-2 are not recommended for interpretation if the parent scale is not clinically elevated. Finally, the MMPI-2-PI was further evaluated and compared to the MMPI-2 and MMPI-2-RF through two medico-legal case examples. These two case examples illustrated the discriminatory difficulties inherent in making diagnositic (or psychiatric) interpretations as opposed to behavioural (or psychological) interpretations, providing further weight to the argument that self reported psychosocial assessment devices should not be used for, or evaluated as diagnostic tools. Additionally, the MMPI-2-PI demonstrated clear delineation and clarification in identifying the constructs being measured without any notable loss of information while also demonstrating the advantages the weighted items have in effective scale endorsement. While the MMPI-2-PI could not be recommended
for use outside of a medico-legal setting, this structure demonstrated it could provide a more effective and efficient psychosocial assessment of personal injury litigants when compared to the MMPI-2 and MMPI-2-RF.